The object of the invention is a method and arrangement for the pumping of a material used in the industry, such as graphite or a certain partial component of a material composition, in which method the material to be pumped is first pre-pressurised prior to the actual pumping event carried out on the material, in order to balance the yield of the pumping arrangement.
In the steel industry, rolling technology is used to manufacture steel plates, strip, pipes, and various profiles. Oils or other friction reducing lubricants are applied between the rolls and the material to be rolled in order to reduce friction. The use of lubricant and successful lubrication improves the uniformity of the rolling result and prevents the rolls from wearing.
In hot rolling, the temperatures are around +1000xc2x0 C., and the rolls must often be cooled with ample amounts of water. Thus the oil used as a lubricant will remain on top of the water film and the lubrication result will deteriorate, simultaneously causing problems with the rolling quality. An unevenly rolled steel strip is rolled thinner by cold rolling, but rolling mistakes generated during hot rolling cannot always be corrected by cold-rolling. Thus the product will contain quality faults which mean additional waste costs for the manufacturer.
The U.S. Pat. No. 4,201,070 presents the use of graphite-water solutions in the manufacture of seamless pipes. The U.S. Pat. No. 5,638,893 presents a lubricant system, with which a continual flow of lubricant is achieved, as well as a multitude of nozzles connected to the system, and each of the nozzles can be directed separately. Moreover, it presents a nozzle moving system, which enables continual lubrication, grouping of nozzles into combinations, and automatic cleaning of nozzles at specified intervals. The U.S. Pat. No. 5,090,225 presents a method where oil-water solution is sprayed in the roll gap from both sides of the metal strip.
Laboratory tests have shown the graphite-liquid solution to be a better lubricant in the rolling process than the oil-based lubricant currently in use. The graphite-liquid solution reduces friction better than other lubricants, and its temperature stability is good. The chemical composition of graphite is carbon. The implementation of graphite as a lubricant has been prevented by the strong wear it causes to pumping equipment. In the procedures tested, graphite is sprayed via high-pressure pumping equipment, for example, on the rolling surfaces via several sapphire nozzles in order to spread the graphite evenly. The problem of this procedure is the wear of the pumping equipment parts, because the graphite particles grind the valves and other parts of the equipment. This results in the uneven spraying of graphite and in a greater demand on maintenance, and therefore, in high maintenance and downtime costs. In certain applications, where an exact dosage of partial components is required, excessive gas within the liquid circuits is the problem. Similarly, high pressure existing in certain pumping arrangements expands the flexible pipelines of the arrangement from time to time and causes leakages in packings and gaskets, etc. The above-mentioned adverse factors affecting the volume flow render it more difficult to maintain the yield of the prior art pumping arrangement at a uniform level.
In some industrial applications, the consumption of the material to be pumped is small and, in addition to that, the correct dosage of the material in relation to another partial component to be pumped is critical for the manufacture of the product. For example, in the manufacture of thin, shaped surgical gloves, the proportions of partial components to be sprayed are very accurately determined. The deviation in the mutual proportions of the partial components must not exceed a couple parts in thousand for the product to fulfill the requirements set. The manufacture of such products set very high demands on the pumps used in the processes, and especially on the evenness of their yield with regard to time. The U.S. Pat. No. 4,844,706 presents a procedure where an arrangement of two membrane pumps is used to achieve a uniform yield in the spraying nozzle connected in the system. The membrane pumps are controlled with the help of xe2x80x9cOPEN-SHUTxe2x80x9d valves controlled by external control logic. The problem with the valves in question is the slowness caused by their structure due to which the pressure only changes after a certain delay after the valve is opened. The U.S. Pat. No. 5,205,722 presents an arrangement where three membrane pumps are used to achieve a uniform yield of the liquid to be pumped. The pumping arrangement is controlled by a partially mechanical rotating cylinder system. It is especially difficult to make the joint yield of the pumps to remain constant in a situation where the pump pumping the liquid to be pumped is replaced by another pump in the pumping arrangement. Replacing a pump in the working phase by another causes a change in the volume flow, which in turn causes decrease in yield in the output circuit which, in some cases, will lead to a deterioration of quality in the end product.
The objective of the invention is to reduce the above-mentioned adverse effects relating to the prior art.
The pumping method for material in accordance with the invention is characterised by the fact that the pumping arrangement to be pre-pressurised is a chamber pump arrangement in which the entry chamber of the chamber pump between the filling stage and the working stage of the chamber pumps is pre-pressurised with the help of the working liquid to a pressure determined in advance.
The pumping arrangement for material in accordance with the invention is characterised by the fact that the pumping arrangement consists of two adjoined chamber pumping arrangement and their control system.
Some advantageous embodiments of the invention have been presented in dependent patent claims.
The basic idea of the pumping method and arrangement in accordance with the invention is as follows: the pumping arrangement consists of a separate, assisting working liquid circuit and of the pumping circuit of the material to be pumped. Thus the possible wearing, corrosive and other disadvantageous properties of the material to be pumped do not have an influence on the working liquid side. An arrangement of two or more chamber pumps is used for the pumping of material and, in this pumping arrangement, the entry chamber of each chamber pump is subjected to a short pre-pressurising after the filling stage in order to guarantee a uniform yield. The arrangement in accordance with this method may contain several pumping arrangements in accordance with the invention, connected in parallel. This method is suited both for low and high-pressure pumping. Pumping can be monitored and controlled specifically for each operation point, in which case the pumping of liquid remains highly controlled at all times. These properties make the liquid pumping arrangement in accordance with the invention free of maintenance, which means that standstill time in the manufacturing process is significantly reduced.
The advantage of this invention is that it enables the yield of the liquid to be pumped to have significantly smaller variations than methods according to the prior art.
A further advantage of the invention is the fact that a pumping arrangement in accordance with the invention is able to pump highly wearing liquid solutions dozens of times longer than prior art pumping arrangements before maintenance is required. Thus significant savings in costs can be achieved in the heavy metal industry.
Another advantage of the invention is the fact that a certain embodiment of the pumping arrangement can be used in applications where a part of the equipment/parts of the process are energised to more than 100 kV.